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Neutrophils, T-lymphocytes and a red blood cell, coloured scanning electron micrograph (SEM). Neutrophils are involved in inflammation and other immune responses. They assist in cellular defence (phagocytosis) of pathogenic microorganisms. A neutrophil destroys an antigen by engulfing it and injecting lethal chemicals. Macrophages will arrive later to consume any remaining debris. Lymphocytes are involved in the specific immune response and are composed mainly of precursor T cells (pre-T cells) and B cells. Pre-T cells circulate in the blood before migrating to the thymus where they develop into specialized cells (helper T cells and killer T cells) that are able to identify antigens and infected tissue cells. Platelets are blood cell fragments that play an essential role in blood clotting and wound repair, and can also activate certain immune responses. Magnification: x1,600 when shortest axis printed at 25 millimetres.